This sample consisted of subjects from two large-scale longitudinal studies:43, 46 the NESDA (Netherlands Study of Depression and Anxiety)49 and the NTR (Netherlands Twin Register).50 The mean ages of cases (N=1738) and controls (N=1802) were 43 and 45 years, respectively. Inclusion criteria for MDD cases were a lifetime diagnosis of Diagnostic and Statistical Manual of Mental Disorders 4th Edition MDD,1 age of 18–65 years and self-reported Western European ancestry. Inclusion criteria for control subjects were no report of MDD at any measurement occasion and low genetic liability for MDD based on survey data measuring MDD-related traits. In addition, controls and their parents were required to have been born in the Netherlands or Western Europe. Only one control per family was selected.
